1. Field of the Invention
The present invention relates to a fuel injection apparatus, and particularly to a solenoid valve unit for a fuel injection apparatus, and more particularly to a solenoid valve unit for a fuel injection apparatus that provides appropriate control of cylinder fuel pressure in a gasoline injection system during engine stamp and normal engine operation.
2. Prior Art Statement
With a conventional cylinder fuel injection system, when the engine has been stopped and is restarted while still hot (i.e., a hot restart), problems have been caused by fuel (gasoline, for example) being vaporized in the fuel piping owing to the high temperature in the engine compartment. This has led to a demand for a system that can maintain stable fuel pressure and prevent fuel vaporization during a hot restart. In particular, when a high-pressure pump driven by the rotation of the engine is used to inject fuel, at low engine speeds the fuel injection amount decreases, making it difficult to prevent fuel vaporization during a hot restart.
JPA 5-321782 discloses a fuel injection apparatus that is able to maintain a constant pressure on the intake side of a high-pressure pump by providing a pressure control valve between a high-pressure pump and a low-pressure pump, and returning fuel from an overflow valve in the high-pressure pump to the pressure control valve. Mechanical pressure flow control valves have been disclosed, such as, for example, by JPA 60- 56872. These mechanical pressure valves are arranged so that fuel is injected via a common rail when the pressure of the fuel being delivered from the pump exceeds the force exerted by a valve spring.
An object of a first aspect of the invention is to provide a solenoid valve unit for a fuel injection apparatus that suppresses fuel vaporization when an engine is subjected to a hot restart and reliably improves engine operation, by providing a stable fuel delivery when the engine is started.
A further object of the first aspect of the invention is to provide a solenoid valve unit for a fuel injection apparatus that can pump fuel at low pressure when the engine is started and change over to high-pressure delivery during normal engine operation.
A further object of the first aspect of the invention is to provide a solenoid valve unit for a fuel injection apparatus that can pump fuel at low pressure when the engine is started and change over to high-pressure delivery during normal engine operation, in which the cost can be reduced by using a single solenoid valve to comprise the solenoid valve unit.
A further object of the first aspect of the invention is to provide a solenoid valve unit for a fuel injection apparatus in which the timing of signals sent to a solenoid valve can be simplified and the solenoid valve opened and closed with a small force, wherein once a control signal has been used to open the solenoid valve, the open state can be maintained when the valve is receiving fuel delivered under high pressure without having to continue to supply control signals.
Further second, third and fourth aspects of the invention are described following the description of thee embodiments relating to the above aspects of the invention.